Tamperproof switch

ABSTRACT

A tamperproof switch in which the tamperproof feature includes a blocking element biased to a blocking or locking position behind blocking lugs of the switch housing. The blocking element and lugs cooperate to prevent movement of a pivotal switch actuator until the blocking element is depressed to a position beyond the blocking lugs. This is readily accomplished with a special two tine key which engages the blocking element on both sides of the post along which it can move. The key and actuator are so arranged that insertion of the key to depress the blocking element moves the key to a position in which it is connected with the actuator so the actuator can be pivoted by the key to change the operating state of the switch. Tipping the blocking element by attempting to depress it with an unauthorized object causes it to lock on the post.

United States Patent 11 1 Carlson l TAMPERPROOF SWITCH Ernest ReinholdCarlson, Fairfield, Conn.

[75] Inventor:

[73] Assignee: Harvey Hubbell, Incorporated,

Bridgeport, Conn.

[22] Filed: Aug. 2, 1974 [21] App]. No.1 494,319

Primary ExaminerHerman Hohauser Attorney, Agent, or-Firm -lerry M.Presson 4 1 Sept. 16, 1975 l 1571 ABSTRACT A tamperproof switch in whichthe tamperproof feature includes a blocking element biased to a blockingor locking position behind blocking lugs of the switch housing. Theblocking element and lugs cooperate to prevent movement of a pivotalswitch actuator until the blocking element is depressed to a positionbeyond the blocking lugs. This is readily accomplished with a specialtwo tine key which engages the blocking element on both sides of thepost along which it can move. The key and actuator are so arranged thatinsertion of the key to depress the blocking element moves the key to aposition in which it is connected with the actuator so the actuator canbe pivoted by the key to change the operating state of the switch.Tipping the blocking element by attempting to depress it with anunauthorized object causes it to lock on the post.

6 Claims, 8 Drawing Figures TAMPERPROOF SWITCH This invention relates tokey opera-ted switches known in the art as tamper-proof" switches. Moreparticularly, the invention relates to a tamper proof operatingmechanism for an electric switch which requires a standard two-prong keyfor its operation.

Tamper proof switches of various types are well known. Characteristic ofsuch switches is a recessed actuator which prevents manipulation of theswitch without some tool, usually a special key which is designed tooperate any one of a number of such switches. Typical of such switchesis a key guide with a slot through which the key is inserted to coupleit to the actuator. so that the actuator can be moved as the key ismoved along the slot, to change the operating condition of the switch.Prior attempts to provide a tamper resistent switch have resulted inconstructions where the key is of a tortuous or irregular shape, andwhen inserted, the key aligns with a similarly shaped passage way in thekey guide. In another known construction, the key is simply a two-prongkey which engages in a recess in the switch actuator to provide thenecessary coupling to move or toggle the actuator. These recess and slotarrangements, while reasonably effective to prevent unauthorizedoperation of the switch, have not been exceedingly difficult to defeatby using a stiff wire or a narrow strip of metal.

Correspondingly, an object of the present invention is to provide a newand improved tamper proof switch adapted to be operated only by aspecial key, preferably of the two-prong type. and in which the tamperproof arrangement positively prevents unauthorized operation by suchdevices as nails, wires, screwdrivers, knives, and the like.

Another object of the invention is to provide a tamper proof operatingmechanism for an electric switch which requires the use of a rigid keywith two prongs in order to disable a blocking or locking deviceassociated with the actuator and which positively prevents switchingmovement of the actuator unless the authorized key is used.

An additional object is a tamper proof switch with a blocking elementbiased toward an actuator locking position by a spring of sufficientstrength that a rigid two-prong key is required to depress the blockingelement to a disabled position where the actuator is coupled to the keyand can be moved to cause the switching action.

An additional object is a unique switch assembly including a blockingelement so arranged in conjunction with the switch housing thatdepressing one side only of the blocking element causes the blockingelement to lock in its blocking position with the result thatunauthorized actuation of the switch is effectively prevented.

A further object is a unique blocking arrangement for a tamper proofswitch where the tamper proof feature takes the simple form of a springand a blocking element in the form of an aperturcd flat metal elementhaving tabs which engage projecting blocking lugs of a switch housingpart to prevent moving the actuator from one position to another untilthe locking element is depressed to a position beneath the blocking lugsof the housing with an authorized key.

The objects described above are realized by providing a spring urgedblocking element within the switch actuating mechanism which cooperateswith a portion of the switch housing to positively prevent movement ofthe actuator unless a special key is used to depress the blockingelement below blocking lugs ofthe switch housing. The special key, inaddition, effectively engages and couples with the actuator in such amanner that the actuator can easily be moved by the key to operate theswitch, after the blocking element is depressed by inscrting the key.

Other objects, advantages, and features of the invention will beapparent from the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial view showing a switch,according to this invention. and a key which is used to operate theswitch;

FIG. 2 is a view in section taken along line 2-2 of FIG. 1 and showingthe switch actuator in one of its extreme positions in which the switchcontacts are open;

FIG. 3 is a view corresponding to FIG. 2 and showing the switch actuatorin its other extreme position in which the switch contacts are closed;

FIG. 4 is a pictorial view of a blocking element, according to theinvention;

FIG. 5 is a partial view in section taken along line 55 of FIG. 2;

FIG. 6 is a view in section taken along line 6-6 of FIG. 2;

FIG. 7 is a view in section taken along line 7-7 of FIG. 6; and

FIG. 8 is a partial view corresponding to FIG. 2 and showing the use ofthe key to switch the actuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings, FIG. 1 shows a typical embodiment of a tamper proof switchassembly 10 according to the invention. Switch I0 comprises a housing orsupport including a base 12 with a cover 14, both formed from aninsulating material. Cover 14 has a recess corresponding to theconfiguration of a body portion 16 of a mounting strap 18 of the typecustomarily used to secure the switch assembly 10 to a mounting box (notshown). Secured to mounting strap 18 and forming part of the housing isa key guide 20 of insulating material having a centrally located keyreceiving slot 22. Slot 22 is of a width to receive and guide a twoprong end 24 of a switch operating key 26 which is positioned as shownat FIG. I, for insertion through the slot. The width of slot 22 is onlyslightly greater than the thickness of key 26.

Key 26 can have another bifurcated end 28 with rounded tines or prongs30. The two prong end 24 having tines 32 with their respective outeredges 34 generally parallel is used to operate an AC tamperproof switch.At the other end of key 26, the tines 30 with rounded sides are foroperation of a DC tamperproof switch.

While the switch described and shown herein is a typical embodiment ofan AC tamperproof switch. it will be appreciated that the invention canreadily be used with a DC type tamperproof switch, with minormodification, and without departing from the scope of this in vention.

As shown at FIG. 2, the body portion 16 of mounting strap 18 has anopening 36 immediately beneath key guide 20 which generally follows theoutline of the guide but is slightly smaller than the guide. Guidepresents an arcuately curved inside surface 38 along wall 39 in whichslot 22 is formed. Surface 38 is bounded on each side by a side wall 40having a pair of recesses 41 and 42 (FIGS. 2 and 3) which defineacentrally located generally v-shaped blocking lug 44 which is integrallyformed with key guide 20. The respective side walls 40 are in parallelplanes on opposite sides of slot 32 (FIG. 6).

Mounted within housing 12, for pivotal movement about a predeterminedaxis extending transversely of the housing is a switch acutator 46.Actuator 46 is moveable between one extreme position in which switchcontacts 48 and 50 are closed, as shown at FIG. 3, and another extremeposition in which a switch operating cam 52 of the actuator engages aleaf type moveable contact arm 54 of the moveable contact 48 to open thecontacts, as shown at FIG. 2.

Actuator 46 has an over-center toggle action as a result of a helicallywound compression spring 55. The lower end of spring 55 extends over acylindrical projection 56 on bottom wall 58 and seats on edges 57 whichflank the projection of the housing. The upper end of the spring seatson a washer 59 on a cylindrical inner tip 60 of actuator 46. The edges57 permit the lower end of the spring to pivot, and edges 61 which flanktip 60 permit washer 59 and the upper end of the spring to pivot.Compression spring 55 provides a toggle action which urges actuator 46toward one or the other of its two extreme positions in which the switchcontacts are either open or closed.

Mounted within the housing on supports 62, and 64, integral with thehousing, are cushion buttons 66 and 68 respectively. These buttons aredimensioned and positioned to be engaged by stop surfaces 70 and 72respectively of the actuator to cushion the actuator at each extreme endof its movement and thereby make the switch operation essentiallysilent.

Acutator 46 has arcuate cars 76 and 78 at each side of a centrallylocated post 80. Ears 76 and 78 are each arcuately curved and areclosely adjacent the curved inner surface 38 of guide 20. The cars havea width slightly less than the distance between the side walls 40 of keyguide 20. As a result of these clearances, the actuator can pivotbetween its extreme positions.

At the inner end of post 80 is an annular recess 82 (FIGS. 2 and 3)which provides a seat for a helical compression spring 84. Seated on theupper endof spring 84 is a blocking element 86 mounted on post 80 andhaving a central opening 88 through which post 80 extends. Blockingelement 86 has a body 89 of generally rectangular exteriorconfiguration. (FIGS. 4,5 and 6) and has locking tabs or stops 90 and 92of a width less than the body at its opposite sides and which project ina direction transverse to the direction of movement of actuator 46. Thelocking tabs 90 and 92 project beyond the sides of the actuator and intoeither recesses 41 or recesses 42 depending on the position of theactuator. Opening 88 is formed by coining the metal of locking bar 86 toform a collar 94 projecting toward recess 82 and which presents a sharpinside corner 96. The diameter of opening 88 is only very slightlygreater than the diameter of post 80. Locking tabs 90 and 92 each have awidth which is slightly less than the width of recesses 41 and 42. Thisdimensioning enables tabs 92 and 90 to seat in the respective recessesagainst either surfaces 98 or surfaces 100 of blocking lugs 44,depending on the position of the acutator.

As is shown at FIGS. 5 and 6, the distance between the outer edgesl02o'ftabs 90 and 92 is slightly less than the distance between the"inside surfaces 103 of either recesses 4 1 or 42. In addition, thedistance between edges 104 and 106 of the body of blocking element 86locking bar is slightly less than the distance between the innersurfaces of the walls 40 of the key guide 20. Correspo ndinglyQwhenlocking bar 86 is depressed (FIG. 8) so its outer or upper surface 108is below the inner end of blocking lug 44, actuator 46 can beswitchedfromone position to another.

'Such depressing of blocking element 86 against the action of spring 84requires that blocking element 86 be engaged simultaneously at twolocations 109 and 110 (FIG. 5) on opposite sides of post 80 in a planeperpendicular to post 80. Blocking element 86 is readily depressed byusing end 24 of key 26. With the key inserted through slot 20 (FIG. 8)and blocking element 86 depressed to a position beneathblocking lug 44,movement of the key along the slot causes the actuator 46 to switch fromone of its extreme positions to the other. The edges 34 of end 24 of thekey engage against the side surfaces 111 and 112 respectively of cars 76and 78 to connect the key to the actuator and permit movement of theactuator against the action of the compression toggle spring 55 whichholds the actuator in either of its extreme positions. 7

Unauthorized operation of the switch is effectively thwarted by theblocking element 86 and the blocking lugs 44. Any attempt to operate theswitch for example by using an unauthorized object suchas a nail orscrewdriver which engages only one side of blocking element 86 willcause the blocking element to tip or tilt (as shown in dotted lines atFIG. 3) with respect tolpost 80, and the sharp inner edge 96 of theblocking element will then grip or dig into the insulating material ofpost 80. Correspondingly, it is impossible to depress locking element 86to a position beneath blocking lug 44 without simultaneously engagingthe blocking element on both sides of post 80. Compression spring 84 isof sufficient strength that thin wire or other material which canreadily bebent to, for example, a hair pin shape so both sides ofblocking. element 86' can be simultancously engaged, will haveinsufficient strength to depress the blocking elernent without bending.

Actuator 46 has trunions mounted for pivotal movement in cooperatingbearing halves 122, 124 in cover 14 and base 12 respectively, as shownin FIGS. 6 and 7. After the switch is assembled, the action of togglespring 54 is to urge the actuator toward cover 14 so the trunions of theactuator are forced against the generally semicircualr bearing halfrecesses 122 of the cover. Inward movement of the actuator toward rearwall 58 of the housing is prevented by the bearing surfaces 124of thebase 12.

ing the corners at these edges to engage the surfaces of the. wingstofurther resist depressing the locking bar with an unauthorized object.I

By virtue ,ofthis arrangement where the width of slot 22 is slightlyless-than the diameter of post 80, flat objccts such as a screwdriverare blocked against insertion by the tip of post 80. Unauthorizedoperation using a tube or pipe is also prevented by virtueof thisdimensioning where the post has a diameter greater'thah the width ofslot 22. However, since post 80 has a'uriiform diameter along asubstantial portion of its length; including that portion along whichthe blockingelement 86 can move. and since key 26 can be used to depressthe blocking element without tilting or tipping, the switch can easilybe operated by one having an authorized key. The extent of inwardmovement of the blocking element against the action of spring 84 islimited by engagement of the bottom surface 131 of the blocking elementwith a shoulder 133 surrounding recess 82 (FIG. 8).

In view of the foregoing, it is apparent that a tamperproof lock switch,constructed in accordance with this invention, effectively defiestampering with unauthorized objects, and can be operated only by anauthorized key of the type shown at FIG. 1. While the typical preferredembodiment described herein is for a switch of the AC type, adapted tobe operated with end 24 of key 26, it is, of course, apparent, that bychanging the configuration of post 80 and the space between cars 76 and78, the tamperproof features of this switch can be adapted to a DCswitch requiring the key configuration of end 28 of key 26.

An additional advantageous feature of the switch of this invention isthat upon movement of the actuator 46 to either of its extremepositions, spring 86 exerts an outwardly directed force which tends toeject the key from the switch. This outwardly directed force simplifiesand assures removal of the key from the switch after it has beenswitched from one position to the other. By virtue of the sharp ornarrow tip on blocking lug 44 and the offset location of projection 56at rear wall 58 which retains the lower end of toggle action spring 55,the switch has no stable center position and will always move to one ofextreme positions of H65. 2 or 3 whenever the key is removed. Thisoccurs depending on the position of the actuator, either as a result ofthe off center toggle action of spring 55 or as a result of the actionof spring 84 which forces the tabs 90 and 92 of the blocking elementinto recesses 41 or 42.

While a typical preferred embodiment of a tamperproof switch accordingto this invention has been shown and described in detail, it is apparentthat changes can be made without departing from the scope of thisinvention, as set forth herein and as defined in the amended claims.

I claim:

1. A tamper proof key operated electric switch comprising a housing;

a switch mechanism carried by the housing, said switch mechanismincluding an actuator moveable along a predetermined path to a firstposition in which the switch is in one condition of operation, and asecond position in which the switch is in another condition ofoperation;

said switch mechanism including key receiving means to receive a key formoving the actuator to said positions;

blocking means in the housing;

a blocking element within the housing and moveable withrespect to theactuator to a blockingposition in which the blocking element Icooperates with the blocking means to prevent 5 I movement of theactuator, and

a released position in which the actuator can be moved from one of itspositions to the other; spring means for urging said blocking elementtoward its blocking position; said blocking element having surface meanspositioned for engagement by. a key inserted in said key receiving meansfor moving said blocking element to said released position so that saidactuator can be moved to said positions upon insertion of the key. 2. Atamper proof switch according to claim 1 wherein said blocking meansincludes a pair of blocking lugs at opposite sides of said actuator; andsaid blocking element includes a pair of tabs which in said blockingposition of the blocking element, cooperate with said lugs to preventmovement of the actuator. 3. A tamper proof switch according to claim 1which further includes means mounting said actuator for pivotalmovement;

and

means mounting said blocking element on said actuator for movement withthe actuator; said blocking element presenting a pair of key engagablesurfaces exposed with respect to said key receiving means to enablemoving said blocking element to its released position upon insertion ofa key. 4. A tamper proof switch according to claim 1 wherein said springsupports said blocking element for tilting movement with respect to theactuator; and cooperating means on said actuator and blocking elementfor locking said blocking element against movement to its releasedposition upon tilting of the blocking element. 5. A tamper proof switchaccording to claim 1 wherein said blocking element includes surfacemeans for engagement by a key at two spaced apart locations; said springsupports said blocking element for tilting movement; and means extendingalong the path of travel of the blocking element between its releasedand blocking positions to lock the blocking element against movement toits released position, in response to tilting of said blocking element.6. A tamperproof key operated electric switch comprising housing means;switch contacts within the housing means; an actuator within the housingmeans mounted for pivotal movement to a first position in which theswitch contacts are opened. and second position in which the switchcontacts are closed; means defining a slot opening through the housingmeans for insertion of a key to operate the actuator; blocking meanswithin the housing means;

moved from one of its positions to another;

spring means for urging said blocking element toward its blockingposition;

said blocking element having surface means positioned for engagement attwo locations by a key inserted through said slot for moving saidblocking element to said released position; and

means on said actuator for connecting a key inserted through the slot tothe actuator for movement therewith to pivot the actuator and switch theswitch contacts.

1. A tamper proof key operated electric switch comprising a housing; aswitch mechanism carried by the housing, said switch mechanism includingan actuator moveable along a predetermined path to a first position inwhich the switch is in one condition of operation, and a second positionin which the switch is in another condition of operation; said switchmechanism including key receiving means to receive a key for moving theactuator to said positions; blocking means in the housing; a blockingelement within the housing and moveable with respect to the actuator toa blocking position in which the blocking element cooperates with theblocking means to prevent movement of the actuator, and a releasedposition in which the actuator can be moved from one of its positions tothe other; spring means for urging said blocking element toward itsblocking position; said blocking element having surface means positionedfor engagement by a key inserted in said key receiving means for movingsaid blocking element to said released position so that said actuatorcan be moved to said positions upon insertion of the key.
 2. A tamperproof switch according to claim 1 wherein said blocking means includes apair of blocking lugs at opposite sides of said actuator; and saidblocking element includes a pair of tabs which in said blocking positionof the blocking element, cooperate with said lugs to prevent movement ofthe actuator.
 3. A tamper proof switch according to claim 1 whichfurther includes means mounting said actuator for pivotal movement; andmeans mounting said blocking element on said actuator for movement withthe actuator; said blocking element presenting a pair of key engagablesurfaces exposed with respect to said key receiving means to enablemoving said blocking element to its released position upon insertion ofa key.
 4. A tamper proof switch according to claim 1 wherein said springsupports said blocking element for tilting movement with respect to theactuator; and cooperating means on said actuator and blocking elementfor locking said blocking element against movement to its releasedposition upon tilting of the blocking element.
 5. A tamper proof switchaccording to claim 1 wherein said blocking element includes surfacemeans for engagement by a key at two spaced apart locations; said springsupports said blocking element for tilting movement; and means extendingalong the path of travel of the blocking element between its releasedand blocking positions to lock the blocking element against movement toits released position, in response to tilting of said Blocking element.6. A tamperproof key operated electric switch comprising housing means;switch contacts within the housing means; an actuator within the housingmeans mounted for pivotal movement to a first position in which theswitch contacts are opened, and second position in which the switchcontacts are closed; means defining a slot opening through the housingmeans for insertion of a key to operate the actuator; blocking meanswithin the housing means; a blocking element; means on said actuatormounting said blocking element for pivotal movement with the actuatorand for movement with respect to the actuator, in a direction generallyradially of the direction of pivotal movement of the actuator; saidblocking element being moveable in said radial direction to a blockingposition in which the blocking element cooperates with the blockingmeans in the housing to prevent pivotal movement of the actuator, and; areleased position in which the actuator can be moved from one of itspositions to another; spring means for urging said blocking elementtoward its blocking position; said blocking element having surface meanspositioned for engagement at two locations by a key inserted throughsaid slot for moving said blocking element to said released position;and means on said actuator for connecting a key inserted through theslot to the actuator for movement therewith to pivot the actuator andswitch the switch contacts.